The present invention relates to a tubeless pneumatic vehicle tire which is resistant to air permeability in the absence of a rubber innerliner. More particularly, the present invention relates to a tubeless pneumatic vehicle tire in which the rubber coating of the innermost body ply is formed from a rubber composition which is resistant to air permeability.
Conventional tubeless pneumatic vehicle tires generally contain a relatively large number of separate components including a tread, subtread, undertread, reinforcing belts or belt plies, sidewalls, abrasion strips, beads, bead fillers, one or more body plies and a relatively air impermeable innerliner. In addition, these components have different physical property requirements and therefore require different rubber compounds. It will therefore be readily apparent that the manufacture of a tubeless pneumatic tire is a costly, time consuming, multi-step process which involves the preparation of a number of rubber compounds of differing formulations; the conversion of the rubber compounds into tire components such as treads, sidewalls, body plies, etc by various methods such as extrusion, calendering, milling, etc.; and the assembly of the tire components into tire form by a tire builder. Moreover, while efforts have been and are being made to automate the tire building process, much of the assembly process is still conducted manually by the tire builder.
Accordingly, it will clearly be evident that either a reduction in the number of rubber compounds or the number of tire components or both would result in a significant reduction in the time and costs involved in the manufacture of the tire. As a consequence, those skilled in the tire art have increased their efforts to simplify the tire manufacturing process.
One approach which involves both a reduction in the number of different rubber compounds and tire components is described in published Canadian patent application no. 2,021,778 to Stevens et al having a publication date of Jan. 26, 1991. This published application relates to a pneumatic vehicle tire having a tread strip, a reinforcing belt, two sidewalls, a carcass that is anchored in beads by being looped about bead cores that are pull-resistant and/or resistant to compression, and respective profiled inner elements that are disposed radially outwardly of the bead cores. The application discloses that at least one of the elements of tread strip, sidewalls, profiled inner elements, beads and rubber coatings for the belt, carcass and bead cores is formed of a rubber mixture comprising 30 to 100% by weight of a nitrile group--containing hydrocarbon rubber having a double bond proportion of no greater than 13 per 100 carbon atoms. The application further discloses that the use of this rubber mixture allows one to employ only three rubber compounds in the tire; that due to the extremely high air impermeability of the rubber mixture the conventional rubber innerliner can be eliminated and that certain other components such as belt covers and bead reinforcing inserts can also be eliminated.
Rubber innerliners are utilized in tubeless pneumatic tires because of their high resistance to air permeability. The innerliner is not wrapped around the bead cores but extends from bead to bead covering only the inner periphery of the tire. This is consistent with its basic function which is to prevent permeability of air through other tire components such as body plies, sidewalls, etc. Conventional rubber innerliners are generally composed of highly saturated rubbers such as butyl rubber, halogenated butyl rubbers or blends of butyl rubbers with small amounts (e.g. 10% by weight or less) of natural rubber.
The use of such rubber innerliners in tubeless tires while beneficial in preventing air permeability presents a number of significant disadvantages. Thus, the use of a separate rubber innerliner requires the preparation of an additional rubber compound and the assembly of an additional tire component during the tire manufacturing process. In addition, such rubber innerliners because of the highly saturated nature of the butyl rubbers employed therein generally exhibit minimal adhesion to other tire components. Moreover, the use of a separate rubber innerliner adds approximately 1.5 pounds to the total weight of the tire.
Accordingly, the elimination of the separate rubber innerliner used in tubeless tires while maintaining satisfactory resistance to air permeability would provide significant advantages particularly in reducing labor costs and total tire weight.